1. Field of the Invention
The present invention relates generally to a fluid flow engine comprising a shaft, a bearing housing for supporting the shaft lubricated through at least two lubricating bores, which lead to at least one shaft bearing shell. The lubricating bores present a predetermined geometry with respect to diameter, length and angular arrangement. There is further a turbine housing for accommodating a turbine wheel mounted on the shaft and rotating in a turbine space of the turbine housing which is attached to the bearing housing.
If the term “fluid flow engine” is used in the context of the present description, it should either mean a turbine or a secondary air pump or the like. Preferably, it is a turbo-charger.
2. Related Art of the Invention
The problem of the development of noise in fluid flow engines is known. Correspondingly, a variety of suggestions have been made for muffling this noise. Muffling arrangements have partially been provided on or around the blades of a rotor, as disclosed in U.S. Pat. Nos. 5,110,258; 5,173,020; 5,820,348 and 6,309,176 or in EP-0 039 459. Other suggestions get at providing mufflers at the flow entrance or flow exit of a bladed rotor. Examples may be found in U.S. Pat. Nos. 3,578,107; 4,204,586 and 4,969,536 or in EP-0 573 895.
All these measures result in a decrease in development of noise, but there is still some noise remaining whose origin is not always clear.